HTLV receptor expression on CD4⁺ and CD8⁺ lymphocyte subsets requires T-cell–receptor stimulation.

(A) Expression of the HTLV Env receptor on Jurkat T cells was assessed using a truncated receptor-binding domain (RBD) of HTLV Env tagged with the Fc domain of rabbit IgG (H_RBD). Cells were then incubated with an FITC-conjugated sheep αrabbit IgG antibody and binding was detected by fluorescence-activated cell sorting (FACS) analysis. Similarly, binding of the amphotropic MLV envelope to its receptor was monitored with an amphotropic SU fragment fused to the Fc domain of rabbit IgG (A_RBD). Filled histograms depict binding in the presence of the secondary FITC-conjugated sheep antirabbit antibody alone. (B) CD4⁺ lymphocytes were purified by negative selection and expression of the HTLV Env and amphotropic MLV Env receptors was immediately assessed on the naive (CD45RA⁺) and memory (CD45RO⁺) populations as indicated. Expression of the HTLV Env and amphotropic MLV Env receptors was then monitored on CD4⁺ lymphocytes that had been prestimulated with immobilized αCD3 and αCD28 mAbs (+) for 4 days (upper panels). HTLV Env receptor expression on freshly isolated CD8⁺ lymphocytes and αCD3/αCD28-stimulated CD8⁺ lymphocytes (+) is shown (lower panels). Control binding with the secondary FITC-conjugated antibody is shown in all histograms (filled). Data are representative of results obtained in 5 independent experiments.